Traditionally, the transfers of images, or, as they are known within the industry, decals, are of two types: those which have a dry release and those which have a wet release. This invention is related to decals with wet release. Those which are available in the market, have an image printed on a paper which has previously been covered with a layer soluble in water. When the decal is soaked with water and pressed on a substrate, on the surface of which the image is to appear, this layer dissolves and becomes soft, so that the paper may be removed, usually by sliding or lifting, leaving the image on the desired surface.
The paper on which the image is printed is known as a wet release decal paper, normally made up of a paper of good quality which is coated with a water soluble emulsion, e.g., starch and gum. The paper may have been specially treated in order to neutralize contraction and expansion due to metereological conditions. The coated paper is known as a "simplex" paper. If it is made to adhere to another paper, it becomes a stronger kind of decal paper, known as a "duplex" paper.
The image may be printed on the decal paper with known methods, such as printing, copying or drawing directly or in reverse, depending on the final surface. Normally, the printer begins by application of a coat of lacquer or varnish on the decal paper surface. Thereafter, he prints the image on the lacquer. Instead of printing directly on the decal paper, the image could also be transferred from another paper, on which it had been applied with known methods. Normally, the decal is applied on the desired substrate with the use of an adhesive, varnish, emulsion or solution of special kind, etc. Before applying the decal, it is submerged in water for a short while, whereafter the decal is applied in its exact position and the paper is slid off. The sliding-off results from the dissolution in water of the decal's water soluble layer.
As a variation, a decal paper is also made with a lacquer or varnish coat already over the water soluble layer. On this type of decal paper, it is possible to print directly on the coat of lacquer or varnish.
A transfer resulting from a decal on which the image has been applied directly on the decal paper surface is called a "direct transfer". On the other hand, if the decal has an image which has been transferred from another paper, on which it was originally applied, the transfer to the substrate is called an "indirect transfer."
Dry release decal papers, rather than coating the paper with a water soluble layer, rely on a coating of a dry release material such as silicone, polyethylene, or other material that has little affinity for the layer of lacquer on which the image is to be printed or transferred. After application of the image to the final substrate, the paper backing of the decal is stripped off with the dry release layer adhering to it.
The foregoing description is largely directed to decals carrying images and made in factories to be sold to users who effect the final transfer to a substrate. Such users may be producers of consumer products, e.g., T-shirts, or producers of metal or plastic items onto which instructions, labels or decorations are to be applied by decal, or hobbiests or artists who transfer to canvas, cloth, ceramics, wood or metal. The ultimate user, however, may be involved in part of the manufacture of the decal itself, particularly in indirectly transferring a picture or other image first to the coated wet release decal paper or the dry release decal paper to form the decal itself, and then in transferring same to the substrate.
In addition to the usual wet release paper carrying a water-soluble coating of, e.g., dextrine, starch and/or gum, which acts as a release layer when wetted, it has been suggested to use conventional coated papers, in which the paper is first sized, as with starch, then a coating comprising adhesive binders, pigments such as clay, casein or other fillers, is coated on one or both sides of the paper. Such papers are designed for printing on the coated side resulting in high-gloss printing suitable for magazine covers and art reproductions. When used as a wet release decal paper, the coating serves to minimize penetration of the image into the paper, and on wetting acts to release the paper from the film carrying the image. See Edwards U.S. Pat. No. 3,334,003; Morgan et al. U.S. Pat. No. 3,350,254.
A transfer utilizing a clay (and/or other pigment) coated paper sometimes works well if the coating is easily removed with water, as long as the transfer is indirect and to an opaque surface. However, if transparency is required, or the transfer is direct, the film carrying the transferred image must be thoroughly cleaned. This is due to the fact that not only does the image transfer, but also part of the clay and binder coating on which the image was originally printed. Sometimes even a portion of the paper fibers and pigmentation may transfer. All of this results in a transferred image which is obscured by a semi-opaque white layer. Normally, it is not possible to clean away this layer with water only, and a more potent solution is required. Sodium hydroxide may be utilized for this task, as is mentioned in some of the patent descriptions referring to such transfers.